【剑指 Offer 50. 第一个只出现一次的字符】

矫情吗；* 2023-09-26 16:55 128阅读 0赞

package com.example.demomain.demoleetcode.easy;
    
    import org.junit.Test;
    
    import java.util.*;
    
    import static org.junit.jupiter.api.Assertions.assertEquals;
    
    /**
     *
     * 在字符串 s 中找出第一个只出现一次的字符。如果没有，返回一个单空格。 s 只包含小写字母。
     *
     * 示例 1:
     *
     * 输入：s = "abaccdeff"
     * 输出：'b'
     *
     * 示例 2:
     *
     * 输入：s = ""
     * 输出：' '
     *
     *  
     *
     * 限制：
     *
     * 0 <= s 的长度 <= 50000
     * @author Administrator
     */
    public class FirstUniqChar {
        
        public char firstUniqCharByMap(String s) {
        
            Map<Character, Integer> map = new LinkedHashMap<>(s.length());
            char[] chars = s.toCharArray();
            for (int i = 0; i < chars.length; i++) {
        
                // 统计出现次数
                map.put(chars[i], map.getOrDefault(chars[i], 0) + 1);
            }
            Iterator<Map.Entry<Character, Integer>> iterator = map.entrySet().iterator();
            while (iterator.hasNext()) {
        
                Map.Entry<Character, Integer> next = iterator.next();
                if (next.getValue() == 1) {
        
                    return next.getKey();
                }
            }
            return ' ';
        }
    
        public char firstUniqCharByBoolean(String s) {
        
            HashMap<Character, Boolean> map = new HashMap<>(s.length());
            char[] chars = s.toCharArray();
            for (char c : chars) {
        
                map.put(c, !map.containsKey(c));
            }
            for (char c : chars) {
        
                if (map.get(c)) {
        
                    return c;
                }
            }
            return ' ';
        }
    
        public char firstUniqCharByLink(String s) {
        
            Map<Character, Boolean> map = new LinkedHashMap<>(s.length());
            char[] chars = s.toCharArray();
            for (char c : chars) {
        
                map.put(c, !map.containsKey(c));
            }
            for (Map.Entry<Character, Boolean> entry : map.entrySet()) {
        
                if (entry.getValue()) {
        
                    return entry.getKey();
                }
            }
            return ' ';
        }
    
        @Test
        public void test() {
        
            assertEquals(' ', firstUniqCharByBoolean(""));
            assertEquals('a', firstUniqCharByBoolean("a"));
            assertEquals('a', firstUniqCharByBoolean("ab"));
            assertEquals('a', firstUniqCharByBoolean("abc"));
            assertEquals('b', firstUniqCharByBoolean("abca"));
            assertEquals('z', firstUniqCharByBoolean("z"));
    
        }
    }